Genetic Regulators of Human Melanocytic Neoplasia: Malignant melanoma is the most common fatal skin cancer. Human tumor samples and mouse models have provided insight into pathways that are altered in melanoma, including activation of Ras, blockade of Rb and p53, as well as change n the adhesion molecule repertoire. However, the medical relevance of murine models of melanoma is limited by major differences between mouse and human skin architecture and by the greater ease of transformation of murine cells. No study has yet addressed the necessity of specific genetic elements in the promotion or maintenance of melanoma in human tissue. Our laboratory's recent finding that defined genetic elements (namely activated Ras, dominant-negative p53, activated cdk4) can act in concert to recapitulate invasive human rnelanocytic neoplasia in human skin regenerated on immune-deficient mice allows for studies of the mechanistic basis for human rnelanocytic carcinogen sis. This proposal aims to use this model to determine the role of specific regulatory proteins and adhesion molecules in the promotion of human rnelanocytic neoplasia. First, the role of the Ras downstream regulator B-Raf will be examined by evaluating the effects of a) activated B-Raf mutants and b) the blockade of downstream Ras effectors on the induction of invasive rnelanocytic neoplasia in primary melanocytes in reconstituted human skin. Second we will address the role of the order of genetic alterations in tumor induction using reciprocal temporal induction of dominant-negative p53 and activated Ras. Additionally, we will determine if p53 disruption is necessary/ to sustain rnelanocytic neoplasia. Third, we will use both genetic and biochemical means to modify E- and N-cadheriri activity, to determine their role in tumor invasion. These studies will provide greater understanding of the roles of Ras, p53, and cadherins in the pathogenesis of rnelanocytic tumors, and may provide targets for therapeutic intervention in human melanoma.